1. Field of the Invention:
The present invention relates to an ignition timing sensor for a Diesel engine.
2. Description of the Prior Art:
A system has been proposed which detects an ignition timing of a Diesel engine by detecting a combustion light of the Diesel engine to feedback controllably a fuel injection time and an injection amount and provide a proper ignition timing for maximizing the performance of the engine. In this system, it is very important to accurately detect the ignition timing as a feedback control factor. For example it is considered that an optical conductor or an optical glass as an optical conductor is provided near the axial center of a glow plug for preheating combustion air to extend through said plug so that the ignition timing of the engine is to be detected from the combustion light in a combustion chamber of the Diesel engine. Such a constitution of the ignition timing sensor does not need to reserve an exclusive mounting position for the sensor in the combustion chamber and thereby simplifies the construction of the combustion chamber. On the other hand, it is expected that the ignition is not to be accurately detected as by viewing a large chamber through a small window when the combustion light in the combustion chamber has to be detected through the glow plug having small diameter relative to the size of the combustion chamber and the optical fiber having still smaller diameter and embedded in said plug.
Further it is suggested that the input end of the sensor is positioned where it is washed by an injection fuel from an injection nozzle in order to remove deposits at the input end. In such a position of the end, however, it is found that when a bad quality fuel, for example the fuel containing a large amount of sulfur, is used or an exhaust gas is recirculated, disadvantages in the center end stained by the deposits of solid components of fuel or the exhaust gas is more than advantages in the washing effect of the sensor by a fuel jet.